1. Field of the Invention
The present invention relates to an ultrasonic probe and an ultrasonic transmitting and receiving apparatus to be used for observing internal organs in a living body, etc. by transmitting and receiving ultrasonic waves.
2. Description of a Related Art
Conventionally, in order to acquire a three-dimensional image by transmitting and receiving ultrasonic waves, two-dimensional images with regard to cross sections in a depth direction are acquired by using a one-dimensional sensor array having a position sensor to electrically steer the received ultrasonic waves, and further, a three-dimensional image is constructed by combining the plural two-dimensional images acquired by mechanically moving this one-dimensional sensor. However, by this technique, since there is a time lag in the mechanical movement of the one-dimensional array, the plural two-dimensional images at different times are combined and the composite image results in a blurred image. Therefore, this technique is unsuitable for imaging of an object accompanied by motion, such as a living organism.
In order to overcome such defects, it is more advantageous that a three-dimensional image is acquired by using a two-dimensional sensor array. However, since the number of ultrasonic detecting elements included in the two-dimensional sensor array becomes exceedingly larger than that in the one-dimensional array, new problems will arise. For example, when using a two-dimensional sensor array having an order of 80×80 elements, it is ideal that all of the elements are used for receiving ultrasonic waves. However, a problem such that wiring becomes more complicated with the larger number of elements arises in the manufacture of the two-dimensional sensor array. In addition, since there is a requirement for as many channels in the electrical circuit for processing the detection signals, which are obtained by detecting ultrasonic waves by using the ultrasonic detecting elements, as there are ultrasonic detecting elements, the electrical circuit becomes unduly complicated.
Under the circumstances, in order to reduce the number of channels of the electrical circuit for processing the detection signals, a “sparse array” approach is used. In such approach, only a part of the ultrasonic elements, which are included in the plural ultrasonic detecting elements arranged in a two-dimensional manner, are used.
For example, a sparse array, in which 40×40 ultrasonic transducers are provided inside of an aperture of an ultrasonic probe and about 30% of the ultrasonic transducers are used, is disclosed in Richard E. Davidsen et al. “TWO-DIMENSIONAL ARRAYS FOR MEDICAL ULTRASOUND USING MULTILAYER FLEXIBLE CIRCUIT INTERCONNECTION”, IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL, VOL. 45, NO. 2, 1998 March, pp. 338–348.
Further, an arrangement of a sparse array, which is considered so that a high-quality sound field may be obtained by reducing side lobes, is disclosed in Richard E. Davidsen et al. “TWO-DIMENSIONAL RANDOM ARRAYS FOR REAL TIME VOLUMETRIC IMAGING”, ULTRASONIC IMAGING 16 (1994), Academic Press Inc., pp. 143–163.
Moreover, in the case where a transducer array having plural ultrasonic transducers is manufactured, the respective ultrasonic transducers are subjected to an inspection as to whether or not they operate with a predetermined performance. If there is only one transducer out of the specifications, that entire transducer array is treated as a defective product. For the two-dimensional transducer array, where the number of ultrasonic transducers is large and the size is smaller than those in the one-dimensional transducer array, the rate of occurrence of defective products is increased.
In the case where an ultrasonic probe is manufactured by using the above described sparse array approaches, the number of ultrasonic transducers to be used is smaller than in the case where all of the transducers inside of the aperture of the ultrasonic probe, are used. Therefore, the rate of occurrence of a defective products can becomes lower due to the smaller number. However, even if there is only one ultrasonic transducer that is out of the specifications among all of the ultrasonic transducers that are to be used in accordance with the design of the sparse array, the transducer array is still treated as a defective product. Thus the yield in the manufacture of transducer arrays continue to be low.